A rail or railway vehicle runs with its vehicle body mounted on a bogie or carriage. At the time of running, air springs are placed between the vehicle body and the bogie to absorb vibration and an amount of air in each air spring is regulated to adjust the height and the tilting of the vehicle body. Patent Document 1 listed below discloses a device arranged to switch over a control valve to supply and discharge compressed air with respect to a pair of left and right air springs, so that the compressed air is discharged from one of the air springs while the compressed air is supplied to the other air spring. By this forcibly changing the height of the left and right air springs, the vehicle body is tilted, compensating cant deficiency during running on a curved track to improve ride comfort.
Patent Document 2 listed below discloses a vehicle body tilting device for rail vehicle arranged to compensate cant deficiency. In particular, this device is configured to transfer compressed air back and forth between left and right air springs. FIG. 9 is a conceptual diagram showing a rail vehicle provided with such a conventional vehicle body tilting device, illustrating a state of the vehicle during running on a curved track. FIG. 10 is a conceptual diagram showing a vehicle body tilting controller. An air pump 105 is placed between left and right air springs 101 and 102 which are individually connected to pipes 106. The air pump 105 used herein is a roots pump designed to provide a flow velocity and a flow rate which are substantially uniquely determined based on a rotation speed and the number of rotations and to rotate reversibly at variable speeds.
When the rail vehicle runs on a curved section where cant deficiency may occur, a reversible variable-speed motor 111 is controlled by a control unit 112 to drive the air pump 105 shown in FIG. 10. Accordingly, the air pump 105 serves to transfer compressed air from the air spring 101 located on the inside of a curve to the air spring 102 located on the outside of the curve. As shown in FIG. 9, the air spring 101 on the inside of the curve contracts, while the air spring 102 on the outside of the curve expands, thereby preventing tilting of a vehicle body 110 caused by a centrifugal force during curve-track running.